1. Field of the Invention
The present invention relates to spray forming polyurethane articles using a rotating spray nozzle.
2. Background Art
Spray forming articles with polyurethane elastomer is a relatively new process that holds much promise for manufacturing high quality, durable parts. Parts that may be made with the polyurethane spray forming process include automotive interior parts as well as other parts. Some automotive interior parts that may be made using a polyurethane skin or a shaped polyurethane layer include instrument panel covers, console covers, inner door panels, glove box covers, floor mats, steering column covers, and knee bolsters, and the like.
Earlier attempts to manufacture polyurethane parts by a spray forming process have required expensive spray nozzle tips that are used to form a conical spray pattern. These elaborate spray nozzle tips, in addition to being expensive, require frequent maintenance and cleaning to assure proper performance. A conical spray pattern yields a slightly cupped spray deposit in cross-section with a portion near the outer edges of the spray deposit being thicker than the central portion.
In a previously filed application, applicants' assignee disclosed a method for spray application of polyurethane to form an article that includes supplying a polyurethane composition to a spray nozzle that sprays the polyurethane composition in a flat fan-shaped pattern onto a mold surface. A swath of polyurethane is applied to the mold surface as the nozzle and mold surface are moved relative to each other in a predetermined path. A skin is created by partially overlapping swaths that are applied in multiple passes of the nozzle relative to the mold. The skin layer formed has a more consistent thickness due to the flat fan-shaped spray pattern in comparison to prior art methods that employ conical spray patterns.
Even with the improvements associated with applicants' prior proposed system, the fan shaped pattern can be irregular and sensitive to the orientation of the robot arm while spraying. There is a continuing need to minimize imperfections in the sprayed coating layer and speed of application. By increasing the rate of material deposition, process cycle times can be reduced. Another aspect of the urethane spray forming process to be improved is to increase control of the spray application in undercut areas of a mold and in highly contoured areas. It would also be advantageous to reduce the difficulty of programming the robot that is used to spray the polyurethane. Finally, it would be advantageous to make the system more robust and error tolerant. To the extent that the positioning of the robot arm can be made less critical, design constraints can be broadened making more parts suitable for urethane spray forming.